System for applying pilot control to the roll gap adjustment of a gauge-controlled cold rolling stand

ABSTRACT

A system of applying pilot control to the roll gap adjustment of a gauge-controlled cold rolling stand. Included in the system are a gauge measuring apparatus for determining the incoming strip thickness, a differential computer for detecting changes in the gauge of the rolled strip, and delay means for the control signal to allow for running time of a point on the strip between the gauge-measuring location and the roll gap. Also included in the control is an evaluation system which takes into account deformation resistance of the rolled stock and of the roll stand constants in determination of the manipulated variable required for adjusting the roll gap.

United States Patent Lautenschlager Mar. 14, 1972 [54] SYSTEM FORAPPLYING PILOT [56] References Cited CONTROL TO THE ROLL GAP UNITEDTATES PATENTS ADJUSTMENT OF A GAUGE- 3,574,280 4/1971 Smith, Jr ..72/s TLE L ROLLING STAND 3,312,092 4/1967 Neumann ..72/13 inventor: HelmutLautenschlager, Grabenstrasse 3,

Hemsbach, Germany Filed: Aug. 3, 1970 Appl. No.: 60,537

Primary Examiner-Milton S. Mehr AttorneyPierce, Scheffler & Parker [5 7]ABSTRACT A system of applying pilot control to the roll gap adjustmentof a gauge-controlled cold rolling stand. Included in the system are agauge measuring apparatus for determining the incoming strip thickness,a differential computer for detecting changes in the gauge of the rolledstrip, and delay means for the control signal to allow for running timeof a point on the strip between the gauge-measuring location and theroll gap. Also included in the control is an evaluation system whichtakes into account deformation resistance of the rolled stock and of theroll stand constants in determination of the manipulated variablerequired for adjusting the roll gap.

3 Drawing Figures EVALUATING Foreign Application Priority Data Aug. 6,1969 Germany ..P 19 40 006.7

US. Cl ..72/8, 72/ 1 6 Int. Cl. ..B2lb 37/00, B21b 37/02, B21b 37/12Field of Search ..72/612, 16, 19-21 GAUGING DIFFERENCE h APPARATUS ECOMPUTER Patented March 14, 1972 3 Sheets-Sheet 5 APW I:

W A pm A Fig. 6

INVENTOR. Helmut Louienschl tiger system for applying pilot control tothe roll gap adjustment of 5 a gauge-controlled cold rolling stand,comprising of gauge measuring apparatus for determining the incomingstrip thickness, a differential computer for detecting gauge changes,delay means for the control signal to allow for the running time of therolled stock between measuring location and roll gap and an evaluatingsystem for taking into account the deformation resistance of the rolledstock and of the roll stand constants when determining the manipulatedvariable required for adjusting the roll gap.

The system is provided for supplementing a gauge-control system in whichdetection of the measured gauge value is subject to dead time. Anexample of such a regulating system is described in a Patent ApplicationP 17 77 154.9 filed in West Germany but the application of the inventionis not confined to such a regulating system. Various regulating systemsand the effect of dead time on the quality of gauge control are examinedin the above-mentioned patent application and in an earlier filed patentapplication P 27 613.8 in West Germany thus dispensing with the need fordiscussing it in this context.

The prior art discloses a plurality of systems for gauge-control some ofwhich also include disturbance-variable feedforward obtained from'thegauge deviation measured on the inlet side. However, dimensioning of thecontrol signal for the most accurate possible gauge correction on thebasis of the deviation measured on the inlet side is subject toextensive uncertainty because the deformation resistance of the rolledstock may vary within wide limits and no reference data of its magnitudeare available.

it is the object of the invention to produce a control signal from themeasured gauge value of the material running into the roll gap, takinginto account the elastic properties of the roll stand and thedeformation resistance of the rolled stock. The control signal thusobtained is delayed in relation to the rolling speed and acts on thestrip thickness by means of the final control element of the regulatingsystem in such a way as to substantially avoid any changes of gauge ofthe emerging strip due to gauge changes of the material running into theroll stand. The accuracy of a gauge control system can thus besubstantially improved. Three different methods may be employed.

According to these methods the invention is characterized by evaluationmeans so constructed that the manipulated variable y (method A) isformed in accordance with the formula y Q x. where K is a constantdepending on the roll stand, Q is a measure of the deformationresistance of the rolled stock and X is a quantity depending on theincoming strip thickness, said manipulated variable being formed bymeans of a multiplier supplied with the quantity Q obtained from aregister to which it is supplied in passes and in accordance with acontrol signal obtained from a computer circuit which determines thequantity Q in accordance with the formula where x is a quantity whichdepends on the gauge of the incoming strip, B=a/K and B=b/K beingconstants which K resi aetity hasgqsqaas with the m lalated to the rollstand, Ag being the change of manipulated variable and Ali, Mr M is thechange of rolling force, the quantity K Q being supplied to themultiplier from a register into which it is supplied in passes and inaccordance with a control signal from a computer circuit whichdetermines the quantity K Q in accordance with the formula gister intowhich it is fed in passes and in accordance with a control signal from acomputer circuit which determines the AP s LiAlLAA. wheregA h h h,refers to the change of gauge of the emerging strip, the change ofrolling forceAP P P and the gauge changeh, =h, h are determined by therolling force P, and the gauge thickness h, prior to the change ofmanipulated variable are retained in one register each in accordancewith a control signal and are then supplied, together with the values Por P, respectively to the computer circuit immediately after themanipulated variable has changed.

No separate definitions are made regarding the choice of means forperforming the computer and register processes required in this context.Known analogue or digital structural elements or modules may be employedto this end, in particular it is possible for the logic functions to beperformed by means of a digital computer which is adapted for freeprogramming. In the last mentioned case the digital computer may alsotake over the control algorithm for the appropriate gauge control.

FIG. 1 discloses the general embodiment of the invention. Specialembodiments are characterized mainly by the choice of the manipulatedvariable for influencing the strip gauge and by the method selected fordetermining the deformation resistance of the rolled stock.

The differential computer 2 compares two values of the deviationsupplied by the gauge control apparatus 1 and occurring in successionwith respect to time. The differential computer contains a register forthe first measured value and a subtracting circuit for computing thedifference between two measured values. It is the function of thedifferential computer to determine a change of gauge of the incomingstrip referred to a section of length. The deviation itself must notresult in a change of manipulated variable: only a change of gauge ofthe incoming strip should produce this result. Expressed in other words,the roll gap may be adjusted by other means (for example manualadjustment) so that the delivered strip is not subject to any deviationdespite deviations from the set value of the incoming strip, the pilotcontrol system may therefore alter the manipulated variable only in theevent of a change of gauge of the incoming strip.

The differential computer 2 may be omitted if the pilot control systemcooperates with a gauge control which constantly biases the manipulatedvariable in the same way as the pilot control system. The regulatingapparatus will then itself produce the necessary equilibrium in the rollgap. In this case it is possible for the deviation from the set value ofthe incoming strip to be transferred directly to the delay circuit 3.The delay circuit 3 delays the signal by a period of time which isrequired by the strip to traverse from the measuring position to theroll gap (final control location). This time is inversely proportionalto the rolling speed v which is supplied to the delay circuit. Thecorrecting period of the final control element may be taken into accountin dimensioning the delay period.

The output signal of the delay circuit 3, that is to say the delayedsignal, is referenced by the letter x. The signal x is the input signalfor the evaluating unit 4. The evaluating unit 4 performs two functions.Firstly the computation and registering of the deformation resistance Qof the rolled stock at the beginning of the pass from the rollingparameters and roll stand constants P, to P fed into the system,secondly the continuous computation of the manipulated variable y bymeans of the input signal x and the stored value of the deformationresistance Q. The starting value of the evaluation unit is themanipulated variable y.

The invention includes three different embodiments of the evaluationunit 4 which operate in each case in accordance with a separate methodfor determining the deformation resistance. These methods and thearrangement resulting therefrom for the evaluation unit 4 are describedin detail hereinbelow. In each case they are approximations of a greateror lesser degree of accuracy but being sufficiently accurate for theintended application as can be easily proved by computation of theerrors.

The slope Q of the plastic characteristic (FIG. 5) is used as a measureof the deformation resistance of the rolled stock. The plasticcharacteristic represents the relationship between the roll gap and therolling force.

All methods designed to determine the slope Q assume the presence on theroll stand concerned of apparatus for measuring the rolling force.

In assuming that the slope Q of the plastic characteristic has beendetermined in some manner, it is possible for the manipulated variable yto be computed in accordance with the relationship ln this expression, Kis a constant, depending on the roll stand and x is a variable which isproportional to the gauge of the incoming strip but is transformed inthe manner described hereinabove (see FIG. 1). The general relationshipspecified herein will be explained in detail by reference to specialarrangements arising from the choice of certain manipulated variables.

Method A for determining the slope Q of the plastic characteristic Thismethod is based on a complete linearization of the plasticcharacteristic of the rolled stock. This slope of the characteristic cantherefore be computed as the quotient of the rolling force P whichoccurs during the rolling operation, and the difference between thegauge of the incoming strip h,; and the gauge of the emerging strip h,,,that is to say,

This is a comparatively rough approximation but detection and processingof the measured value is very simple and accurate (relatively largemeasured values so that any minor fluctuations which are always present,do not have any substantial influence on the result). The arrangement ofthe evaluation unit 4 resulting from this method is illustrated in FIG.2.

The computer circuit 5 is constructed in accordance with known methods.In this computer circuit first forms the difference h h and then thequotient P,,./ (h h,,). The output signal of the circuit 5 is the valueQ which is retained in the register 6. The register 6 is supplied with acontrol signal S which permits registration only for certain operativestates of the roll stand, for example during threading up, and leavesthe register content unchanged during the remaining operating phases.Finally, the multiplier circuit 7 continuously forms the manipulatedvariable y in accordance with the relationship y K Q -x. H6. 2illustrates the number and kind of input variables of the evaluationunit 4 constructed in accordance with the method A.

Method B for determining the slope Q of the plastic characteristic Thefollowing method linearizes the plastic characteristic only in a verysmall zone (differential method). The magnitude of the roll gap ischanged by reference to a defined change of manipulated variable and theresultant change of rolling force is measured. The value of Q may thenbe calculated from the known amount of change of manipulated variable A0and the measured value of the change of rolling force A P in accordancewith the relationship FIG. 3 shows the arrangement of the evaluationunit 4 in accordance with the method B. The register 8 stores the valueof the rolling force P prior to the change of manipulated variable S(control signal). The rolling force has the value P immediately afterthe manipulated variable is changed by the amount dc. The difference APP, P is formed by known methods in the computer circuit 9 and this isused to form the quotient B Ac/AP to which the constant a is added. Theinverse valueof this intermediate quantity supplies the required amountK Q which is retained in the succeeding register 10. The multiplier 11computes the manipulated variable y in known manner.

The number and kind of input variables required for the evaluation unit4 according to method B may be obtained from FIG. 3. The roll standconstants a and B must be defined once, most conveniently bymeasurement.

Method C for determining the slope Q of the plastic characteristic Thismethod is also of the differential kind with a defined change ofmanipulated variable for biasing the roll gap. In this case, the changeof rolling force AP as well as the change of the rolled gauge Ah, as theresult of a change of manipulated variable are measured. Under theseconditions FIG. 4 shows the corresponding arrangement of the evaluationunit 4 according to method C. This method is the most complex because itrequires a register 8 for the rolling force P, (in the same way as inmethod B) as well as a register 12 for the thickness h, of the stripprior to a change of manipulated variable. The index 2 of thesequantities is associated with the values immediately after the change.The computer unit 13 forms the difierence valuesA P P P and Ah, h A 1 hand from this forms the quotient AP /Ah,,. The value of Q is registeredand the manipulated variable y is computed in units 14 or 15respectively in the manner already described hereinbefore.

Some special arrangements according to the invention are describedhereinbelow, the kind of manipulated variable being predetermined.Accordingly, the necessary roll stand constants are also defined ingreater detail.

To roll travel as manipulated variable The roll gap can be influenced inknown manner by the screw-down of the upper rolls. To this end, thecharacteristics of the roll stand can be obtained from the known rollingforce roll gap diagram, shown in FIG. 5.

The rolled stock of thickness h runs into the roll gap and is deformedunder the effect of the rolling force in accordance with the plasticcharacteristic 16, the slope of which is Q at the operating point. Therolling force deforms the roll stand approximately elastically inaccordance with Hooks law; the stretch of the roll gap is indicated bythe straight line 17 having the slope M. The point of intersection ofthe straightline 17 with the plastic characteristic (operating point)defines the rolled strip thickness h Any change ofthe incoming gauge bythe amount Ah results in a parallel displacement of the characteristic16 on the h-axis (new line 16a). In order to maintain the gauge of thedelivered material at a constant value it is necessary for thecharacteristic 17 to be displaced in the opposite direction in parallelto the h-axis and by the amount A s (top roll screw down travel) thegeometrical relationships provide the following change of top rollscrew-down as A Q/M) ME This will take the form of the earlier mentionedgeneral relationship y K Q r if the regulating travel of the top rollscrew-down is used as the manipulated variable. The overall elasticconstant l/M of the roll stand is the constant K which depends on thesaid roll stand.

To obtain the slope Q of the plastic characteristic 16 it is possiblefor the methods A, B or C to be optionally employed. The methods A and Cdo not depend on the kind of manipulated variable and do not thereforerequire any further explanations.

The general equation expressing the value of Q in accordance with methodB when the top roll screw-down undergoes a defined change by the amountc s takes the form of 1 Q 1 As M AP If the gauge of the incoming stripduring the rolling operation varies by the amount h,; by measurement, itwill be necessary for the control apparatus according to FIG. 1 toadjust the top roll screw-down by the amount A As PRELOADING OF THECHOCKS AS THE MANIPULATED VARIABLE This case is based on a design of thestand described in detail in the patent application P 17 77 154.9 and inthe accompanying illustration. This stand is pre-loaded, the preloadingforce acting between the chocks of the backing rolls.

Stands of this kind are known and are not subject of the inven-' tion.

The force roll gap diagram for such stands and according to theinvention is illustrated in FIG. 6.

The screw-down force P loads the roll stand and comprises the reactionof the rolled stock P and the preloading force P Assuming linearconditions, the roll stand will stretch due to P and in accordance withthe straightline 18 having the slope M The chock may be assumed todeform due to the rolling force in accordance with the straight line 19.For the sake of simplicity, the plastic characteristic 20 is alsoplotted as a straight line having the slope Q. The point of intersectionof the straight line 19 with 20 defines the size of the roll gap whichalso represents the delivery gauge h If the gauge of the incoming stripchanges from the value h by the amountAh to the amount h this isequivalent to a parallel displacement of the plastic characteristic from20 to 200. According to the invention the screw-down force P is to bechanged accurately by the amountAP which remains the delivery gauge h,at a constant value. FIG. 6 discloses that under these conditions boththe screw-down force P, as well as the rolling force P must changecorrespondingly, that is to say,

APR P4 The required screw-down force change will then be obtained fromthe geometrical relationships of FIG. 6 as R A/ w)QA This equation canbe simplified still further if due allowance is made for the fact thatthe overall module M of the roll stand is calculated from the modules M,of the stand and M of the roll chocks in accordance with therelationship MA ,M iMw M r AP; 5

This equation can also be derived from FIG. 6. According to theinvention the change of manipulated variable as the result of thecontrol function during rolling will then take the form M "1 a M. M

if the gauge of the incoming strip varies by h. The constants of thegeneral equation in this case are a =1/M,, and B (M /M Iclaim:

ll. A system for applying pilot control to a roll gap adjustment of agauge-controlled cold rolling stand for rolling metal strip, comprisinga gauge measuring apparatus for determining the incoming stripthickness, a differential computer for detecting gauge changes of saidincoming strip and supplying a control signal proportional thereto,delay means for the control signal to allow for running time of therolled strip between measuring location and roll-gap and an evaluatingsystem for taking into account deformation resistance of the rolledstrip and of roll stand constants when determining a manipulatedvariable y required for adjusting the roll gap, said evaluation systemso constructed that the manipulated variable y is formed in accordancewith the formula y K Q x where K is a constant depending on the rollstand, Q is a measure of deformation resistance of the rolled strip andx is a quantity depending on the incoming; strip thickness, saidmanipulated variable being formed by means of a multiplier supplied withthe quantity Q obtained from a register to which it is supplied inpasses and in accordance with another control signal obtained from acomputer circuit which determines the quantity Q in accordance with theformula where P, is the rolling force and h and h refers to the incomingand emerging strip thickness respectively.

2. A system for applying pilot control to a roll gap adjustment of agauge-controlled cold rolling stand for rolling metal strip, comprisinga gauge measuring apparatus for determining the incoming stripthickness, a differential computer for detecting gauge changes of saidincoming strip and supplying a control signal proportional thereto,delay meansfor the control signal to allow for running time of therolled strip between measuring location and roll gap and an evaluatingsystem for taking into account deformation resistance of the rolledstrip and of roll stand constant when determining a manipulated variabley required for adjusting the roll gap said evaluation system which isconstructed so that a multiplier is provided for forming the manipulatedvariable y in accordance with the formula where x is a quantity whichdepends on the gauge of the incoming strip, a a/K and B b/K beingconstants which are related to the roll stand, Ag being the change ofthe manipulated variable and AP P,, 1 is the change of rolling force,the quantity K Q being supplied to the multiplier from a register intowhich it is supplied in passes and in accordance with another controlsignal from a computer circuit which determines the quantity KQ inaccordance with the formula the change of rolling forceAP beingdetermined by the rolling force P prior to the change of the manipulatedvariable and being retained in a register and in accordance with a thirdcontrol signal and is then supplied, together with the rolling force Pto the computer circuit immediately after the change of the manipulatedvariable.

3. A system for applying pilot control to a roll gap adjustment of agauge-controlled cold rolling stand for rolling metal strip, comprisinga gauge measuring apparatus for determining the incoming stripthickness, a differential computer for detecting gauge changes of saidincoming strip and supplying a control signal proportional thereto,delay means for the control signal to allow for running time of therolled strip between measuring location and roll gap and an evaluatingsystem for taking into account deformation resistance of the rolledstrip and of roll stand constants when determining a manipulatedvariable y required for adjusting the roll gap, said evaluation systemconstructed so that a multiplier is provided for forming the manipulatedvariable y in accordance with the formula y K Q I said multiplier beingsupplied with the quantity Q from a register into which it is fed inpasses and in accordance with another control signal from a computercircuit which determines the quantity Q in accordance with the formula QAP /Ah where Ah, h h refers to a change of gauge of the emerging stripand Pw Pw Pwg refers to a change of rolling force, Pw and h beingdetermined from the rolling force P, and the gauge thickness h, prior toa change of the manipulated variable and are retained in one registereach in accordance with a third control signal and are then supplied,together with the values P or P respectively to the computer circuitimmediately after the manipulated variable has changed.

Invezzccfli) HELMUT LAUTENSCHLAGER M. rs certified that error appears inthe above-identified parent and that said Letters Patent are herebycorrected as shown below:

In the: heading of the patent the identity or the a i n e, to wit: IAKTIENG ESELLSCHAFT BROWN,

B FI ,8q cIE'.,. BADEN, SWITZERLAND should appear.

Sigped and sealed this 15th d'ay of August 1972.

(SEAL) At'test;

EDWARD M. FLETCHER; JR ROBERT GOTTSCHALK Att'esting ,Offi'gerCommissioner Qf Patents

1. A system for applying pilot control to a roll gap adjustment of agauge-controlled cold rolling stand for rolling metal strip, comprisinga gauge measuring apparatus for determining the incoming stripthickness, a differential computer for detecting gauge changes of saidincoming strip and supplying a control signal proportional thereto,delay means For the control signal to allow for running time of therolled strip between measuring location and roll gap and an evaluatingsystem for taking into account deformation resistance of the rolledstrip and of roll stand constants when determining a manipulatedvariable y required for adjusting the roll gap, said evaluation systemso constructed that the manipulated variable y is formed in accordancewith the formula y K . Q . x where K is a constant depending on the rollstand, Q is a measure of deformation resistance of the rolled strip andx is a quantity depending on the incoming strip thickness, saidmanipulated variable being formed by means of a multiplier supplied withthe quantity Q obtained from a register to which it is supplied inpasses and in accordance with another control signal obtained from acomputer circuit which determines the quantity Q in accordance with theformula where Pw is the rolling force and hE and hA refers to theincoming and emerging strip thickness respectively.
 2. A system forapplying pilot control to a roll gap adjustment of a gauge-controlledcold rolling stand for rolling metal strip, comprising a gauge measuringapparatus for determining the incoming strip thickness, a differentialcomputer for detecting gauge changes of said incoming strip andsupplying a control signal proportional thereto, delay means for thecontrol signal to allow for running time of the rolled strip betweenmeasuring location and roll gap and an evaluating system for taking intoaccount deformation resistance of the rolled strip and of roll standconstant when determining a manipulated variable y required foradjusting the roll gap said evaluation system which is constructed sothat a multiplier is provided for forming the manipulated variable y inaccordance with the formula where x is a quantity which depends on thegauge of the incoming strip, Alpha a/K and Beta b/K being constantswhich are related to the roll stand, Incrementc being the change of themanipulated variable and IncrementPw Pw1 - Pw2 is the change of rollingforce, the quantity K . Q being supplied to the multiplier from aregister into which it is supplied in passes and in accordance withanother control signal from a computer circuit which determines thequantity KQ in accordance with the formula the change of rolling forceIncrementPw being determined by the rolling force Pw1 prior to thechange of the manipulated variable and being retained in a register andin accordance with a third control signal and is then supplied, togetherwith the rolling force Pw2 to the computer circuit immediately after thechange of the manipulated variable.
 3. A system for applying pilotcontrol to a roll gap adjustment of a gauge-controlled cold rollingstand for rolling metal strip, comprising a gauge measuring apparatusfor determining the incoming strip thickness, a differential computerfor detecting gauge changes of said incoming strip and supplying acontrol signal proportional thereto, delay means for the control signalto allow for running time of the rolled strip between measuring locationand roll gap and an evaluating system for taking into accountdeformation resistance of the rolled strip and of roll stand constantswhen determining a manipulated variable y required for adjusting theroll gap, said evaluation system constructed so that a multiplier isprovided for forming the manipulated variable y in accordance with theformula y K . Q . x said multiplier being supplied with the quantity Qfrom a register into which it is fed in passes and in accordance withanother control signal from a computer circuit which determines thequantity Q in accordance with the formula Q Increment Pw/ IncrementhAwhere IncrementhA hA1 - hA2 refers to a change of gauge of the emergingstrip and Pw Pw1 - Pw2 refers to a change of rolling force, Pw and hbeing determined from the rolling force Pw1 and the gauge thickness hA1prior to a change of the manipulated variable and are retained in oneregister each in accordance with a third control signal and are thensupplied, together with the values Pw2 or PA2 respectively to thecomputer circuit immediately after the manipulated variable has changed.